In Reply.—Dr Weissman's estimates ignore the denominator. United States Department of Transportation studies suggest that the average American driver spends about one hour each day in his vehicle.1 If Dr Weissman is correct in his estimate of time required to use a seat belt, then seat belt use "costs" the individual only 1 s out of every driving minute. For this investment, a driver reduces his likelihood of severe injury or death by at least 50%, if he should be involved in a serious collision.2 The US Department of Transportation estimates that each American has a one in three chance of being involved in such a collision during his lifetime.3 It is this risk, not the 0.0001 claimed by Dr Weissman, that should be considered by individuals. To assess the cost to society, Dr Weissman should consider societal costs such as lost productivity resulting from collisions.